turbofreak

I have both a 07 GXP and a new 08 HHR SS and have tried the launch feature several
times. I agree that it is all in software but it is NOT just a rev limiter.
The HHR SS does not launch as well as GXP because of weight transfer off the front wheels. To this end, the pcm limits the boost in 1st gear to 10 psi, then gives you full
15 psi + in the other gears. The car has a fairly deep 1st gear and without launch
control, it is pretty easy to go up in smoke. Been hard around here with winter to find
dry + clean pavemeent but found some and tried a launch. Hit button on dash twice
and it says "Launch Control" on dash. Put throttle to floor and engine revs to 4100 rpm
and stays there. Side step clutch and be ready to shift in a hurry. You still get wheelspin
BUT here is the difference because the ecm seems to be playing with timing and possibly
something else to modulate the wheel spin to the min needed for a good launch. I was
supprised how well it worked. A really good driver might be able to do about as well by
picking the correct rpm for launch and modulating the throttle but even then he loses
the ecm helping maintain the "correct" wheelspin for max foward acceleration

turbofreak

LT1GMC

Thanks, that is a great observation, sure makes the wait for mine to come in harder. :)

FastedSS

Thanks, I've been waiting to try mine, I've got 1400 + miles so the next time I get a clear road, away we go

In non launch mode I get 12 or 13 psi boost when I hit the rev-limiter. It might be higher, everythings happens so fast it's hard to tell, and the boost guage may just lag what happening.

In first gear with a full throttle all I get is wheel spin, on a dry clean road with warm tires.